Fluid control is routinely practiced within a wide variety of industries. Control is typically achieved using devices that are specifically designed to perform a unique control operation. Examples of such control devices are pressure relief valves, pressure regulators, back-pressure regulators, velocity fuses, mass flow controllers, pilot operated valves, check valves, and shuttle valves.
Pressure is typically communicated from one source to another via the flow of a fluid such as gas or a liquid. Operational challenges arise when the flow used to communicate pressure causes damage to the sealing element that is designed to maintain the desired pressure difference. Damage can occur from the cutting capacity of high velocity fluid streams passing over a device's sealing component during the pressure maintenance operations required to continuously sustain the required differential pressure. For applications that require the maintenance of high differential pressures, devices typically use sealing elements fabricated from durable rigid materials such as metal or thermoplastics. While these materials are durable, they are not pliable. The lack of pliability results in reduced performance in the presence of particulate matter and reduced performance from surface imperfections on the sealing element or the component that the sealing element seals against, i.e., the seat.
For example, a steel ball could never seal a circular steel aperture if a sand grain was wedged between the steel ball and the edge of the aperture (or if the edge of the aperture was slightly nicked). If the ball was made of a pliable material such as rubber, the ball could seal the circular aperture because the sand grain could imbed in the ball and the ball could then fully contact the perimeter of aperture. While the rubber ball is a superior sealing material, it is also highly susceptible to damage from the cutting action of high velocity fluid streams. Thus, a technology gap exists for pressure metering applications that require high differential pressures, particulate insensitivity, and reliable repeatable operation. For applications that require zero leak flow after a pressure differential is established and/or require cyclic operations, the use of rigid seal elements becomes inadequate.
Many valving designs directly, or indirectly, involve three pressures: 1.) inline high pressure source; 2.) inline low pressure source; and 3.) a static pressure source, e.g., atmospheric pressure in a spring cavity. Valve designs that involve an isolated, or sealed, static pressure exhibit limited functionality in a downhole environment. The primary reason is that most downhole operations are performed in a well that is filled with liquid, thus the static pressure increases as a function of depth. This change in static pressure results in a change in valve performance as a function of depth. Valve designs that provide free static pressure communication to all actuating parts within the system enable depth (or static pressure) independence. This is because fluid based valve actuation forces result from differential pressures acting upon an area. Since the actuation forces are based on the difference between pressure sources, the reference pressure (or static pressure) that is common to all sources is canceled out, and the performance of the valve becomes depth independent.
An additional criteria required of downhole fluid control operations is related to size. Wellbores of various diameters are created in an effort to optimize the economic impact of a field development; and valves must be smaller than the wellbore diameter in which they are deployed. As a result, valves with small external dimensions possess a larger portfolio of accessible intervention wells than larger valves of similar function. In addition, when valves are deployed downhole they are not readily accessible for servicing; thus significant expense is typically incurred during the downhole intervention activity. Consequently, small fluid control devices are sought that are static pressure independent systems capable of repeatable, reliable, particulate insensitive performance in service conditions that require high pressure differentials. The remainder of the document will focus on a pressure relief/back-pressure valve that is compatible with downhole service.
Pressure control devices that are designed to maintain high differential pressures by fluid metering past a sealing component are typically constructed using rigid seal materials that are durable when exposed to high velocity fluid jets, or the pressure control devices are de-rated in pressure to the point that more pliable seal materials are acceptable for the specified service conditions. For example, the Circle Seal 5300 pressure relief device is designed to function at differential pressures up to 72 MPa (10500 psi). For these high differential pressures, the seal materials available for this valve are either metal or a rigid thermoplastic. The Swagelok R4 series pressure relief valve is designed to operate at differential pressures up to only 10 MPa (1500 psi). The lower differential pressure rating allows the seal materials for the R4 to be fabricated out of pliable elastomer compounds such as VITON, BUNA N, or NEOPRENE. Both of the aforementioned valves are three pressure systems (i.e., the spring cavity resides at atmospheric pressure).
The Circle Seal 5100 pressure relief valve is a two pressure system that contains a pliable seal material, but the maximum differential pressure rating is only 16.5 MPa (2400 psi). The Kepner 1354 pressure relief valve is a two pressure system that contains a pliable seal material, but the maximum differential pressure rating is only 13.8 MPa (2000 psi). These examples illustrate the inherent conflict between high differential pressure maintenance and reliable sealability in environments that may contain solid particles.
A need exists for valves that will meter pressure effectively in environments, such as downhole environments, that may contain solid particles and in which the ambient pressure to which the valve will be exposed during operation is subject to change, due to factors such as the need to change depths in a downhole environment. An object of this invention is to provide such valves. Other objects will become apparent through consideration of the following specification together with the accompanying drawings.